NimNodeStep = SliceStep[NimNodeIndex]

PreOrderStep = object
  stack: SeqStack[NimNode]
  current: Optional[NimNode]

func indexes(n: NimNode): Stream[NimNodeStep, NimNodeIndex] {...}{.raises: [], tags: [].}

func indexesReverse(n: NimNode): Stream[NimNodeStep, NimNodeIndex] {...}{.
    raises: [Exception], tags: [RootEffect].}

func children(n: NimNode): Stream[NimNodeStep, NimNode] {...}{.raises: [Exception],
    tags: [RootEffect].}

func childrenReverse(n: NimNode): Stream[NimNodeStep, NimNode] {...}{.raises: [Exception],
    tags: [RootEffect].}

func pairs(n: NimNode): Stream[NimNodeStep,
                            tuple[index: NimNodeIndex, node: NimNode]] {...}{.
    raises: [Exception], tags: [RootEffect].}

func preOrderStep(stack: SeqStack[NimNode]; current: Optional[NimNode]): PreOrderStep {...}{.
    raises: [], tags: [].}

func initPreOrder(root: NimNode): PreOrderStep {...}{.raises: [], tags: [].}

func hasMore(self: PreOrderStep): bool {...}{.raises: [], tags: [].}

func generate(self: PreOrderStep): NimNode {...}{.raises: [Exception, UnboxError],
    tags: [RootEffect].}

func next(self: PreOrderStep): PreOrderStep {...}{.raises: [Exception, UnboxError],
    tags: [RootEffect].}

func traversePreOrder(root: NimNode): Stream[PreOrderStep, NimNode] {...}{.
    raises: [Exception, UnboxError], tags: [RootEffect].}